Automated post-pacing interval measurement

ABSTRACT

A method for processing a biopotential signal includes detecting a pacing signal, and applying a dynamic filter on a pacing channel based on the detected pacing signal. A method for processing a biopotential signal includes detecting a pacing signal, and automatically obtaining a post-pacing interval based at least in part on the pacing signal.

FIELD OF THE INVENTION

The present invention relates generally to tissue characterization foridentification of an ablation site, and more particularly, toapparatuses and methods for obtaining post-pacing interval measurement.

BACKGROUND OF THE INVENTION

A normal heartbeat involves generation of an electrical impulse andpropagation of the electrical impulse across the heart, which causeseach chamber of the heart to appropriately contract. Sometimes aberrantconductive pathways develop in heart tissues, and disrupt the normalpath of the electrical impulse. For example, anatomical obstacles orconduction blocks in heart tissue can disrupt the normal propagation ofan impulse by causing the impulse to degenerate into several circularwavelets that circulate about the obstacles, thus disrupting normalactivation within the heart tissue and chambers. Also, slow conductionzones in animal and human hearts constrained by anatomical or conductionblocks are believed to exist. Such a zone is a localized region of theheart tissue which propagates an impulse at a slower speed than normalheart tissue thus sometimes resulting in errant, circular propagationpatterns or reentrant pathways. Reentrant pathways provide thesubstrates for the re-excitation of a region of cardiac tissue by anexcitatory wavefront. Reentry may continue for one or more cycles andmay sometimes result in tachycardia. Reentrant ventricular tachycardia(VT) is an abnormally rapid ventricular rhythm with aberrant ventricularexcitation (wide QRS complexes), usually in excess of 150 per minute,which is generated within the ventricle of the heart as a result of areentrant pathway.

To treat VT, it is desirable first to determine the physical location ofthe aberrant pathways. Once located, the heart tissue in the pathway canbe ablated and destroyed by heat, chemicals, and/or other means. Heatcan be generated in the targeted tissue using, for example, radiofrequency (RF) energy, microwave energy, ultrasonic energy, or lasers toeffect the ablation lesion. Ablation can remove the aberrant conductivepathway, restoring normal myocardial contraction. More specifically, totreat VT, the targeted conduction zone must be located and destroyed (orpartially destroyed), with the goal of eliminating the conduction zone'sability to conduct electrical impulses.

In order to determine the physical location of the aberrant pathways,physicians have performed entrainment mapping. For example, entrainmentmapping of re-entrant tachycardia is often used for identifying criticalpathways of aberrant intracardiac conduction. Concealed entrainment ofan arrhythmia requires that a post-pacing interval (PPI) be obtained.For example, in one protocol, concealed entrainment of an arrhythmiarequires, among other criteria, that a PPI be within approximately 20 msof a tachycardia cycle length. However, existing devices do not allowPPI measurements be obtained efficiently and conveniently. Particularly,when a pacing signal is routed to a biopotential sensing catheter thatis connected to a diagnostic recording system, the biopotentialrecordings from the catheter can be obscured. This can be the result ofthe differential between the pacing signal (e.g., generally in the rangeof tens of volts) and an intracardiac biopotential (e.g., generally inthe range of several millivolts). Recording amplifiers' responses tolarge transient spikes (e.g., step response of a signal processingchain) can also cause a variety of phenomenon, such as, saturation,overshooting, ringing, that can obscure biopotential recordings. As aresult, a user may be required to manually manipulate existing softwareand manually process data in order to obtain a desired informationassociated with a particular biopotential recording.

Furthermore, existing software may automatically clip off valuable dataassociated with signal on a pacing channel, thereby making it difficultfor a user to obtain desired information from a diagnostic recording.FIG. 1 illustrates an example of a display window 100 displaying data102 that are generated using existing systems. Data 104 (shown indotted-line) beyond the display window 100, including valuablebiopotential data 106, are being clipped off by existing softwarebecause they are out of range. In such cases, in order to obtain a PPI,a user may need to modify existing software to search for thebiopotential data 106. After the biopotential data 106 is located, theuser may then need to manually measure or calculate a duration between apace signal and the biopotential data 106 to obtain the PPI. Thislengthens the amount of time necessary to diagnose a patient, and cancomplicate a diagnostic procedure.

Thus, there is currently a need for an improved device and method forobtaining biopotential data, and more specifically, for obtaining apost-pacing interval.

SUMMARY OF THE EMBODIMENTS

In accordance with some embodiments of the invention, a system forprocessing a biopotential signal includes a detector for detecting apacing signal, and a filtering module for applying a dynamic filterbased on the detected pacing signal.

In accordance with other embodiments of the invention, a method forprocessing a biopotential signal includes detecting a pacing signal, andapplying a dynamic filter on a pacing channel based on the detectedpacing signal.

In accordance with other embodiments of the invention, a computersoftware product having a set of stored instructions, an execution ofwhich causes a process to be performed, the process comprising detectinga pacing signal, and applying a dynamic filter on a pacing channel basedon a detected pacing signal.

In accordance with other embodiments of the invention, a system forprocessing a biopotential signal includes a detector for detecting apacing signal, and means for automatically obtaining a post-pacinginterval based at least in part on the pacing signal.

In accordance with other embodiments of the invention, a method forprocessing a biopotential signal includes detecting a pacing signal, andautomatically obtaining a post-pacing interval based at least in part onthe pacing signal.

In accordance with other embodiments of the invention, a computersoftware product having a set of stored instructions, an execution ofwhich causes a process to be performed, the process comprising detectinga pacing signal, and automatically obtaining a post-pacing intervalbased at least in part on the pacing signal.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention. It should be noted that the figures are notdrawn to scale and that elements of similar structures or functions arerepresented by like reference numerals throughout the figures. In orderto better appreciate how the above-recited and other advantages andobjects of the present inventions are obtained, a more particulardescription of the present inventions briefly described above will berendered by reference to specific embodiments thereof, which areillustrated in the accompanying drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an example of an electrogram, particularly showingbiopotential data being clipped off;

FIG. 2 is a block diagram of a system for sensing biopotentials inaccordance with some embodiments of the invention;

FIGS. 3 and 4 illustrate logics of a filtering module and a calipermodule in accordance with some embodiments of the invention;

FIG. 5 is an example of an electrogram obtained using the system of FIG.2;

FIG. 6A is a diagram illustrating entrainment pacing at a site remotefrom a conduction zone;

FIG. 6B is a diagram illustrating entrainment pacing at a site within aconduction zone; and

FIG. 7 is a block diagram of a computer hardware system with whichembodiments of the present invention can be implemented.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments of the present invention are described hereinafterwith reference to the figures. It should be noted that the figures arenot drawn to scale and elements of similar structures or functions arerepresented by like reference numerals throughout the figures. It shouldalso be noted that the figures are only intended to facilitate thedescription of specific embodiments of the invention. They are notintended as an exhaustive description of the invention or as alimitation on the scope of the invention. In addition, an aspectdescribed in conjunction with a particular embodiment of the presentinvention is not necessarily limited to that embodiment and can bepracticed in any other embodiments of the present invention.

FIG. 2 illustrates a mapping system 200 in accordance with embodimentsof the invention. The mapping system 200 includes a sensor 202 forsensing cardiac signals (e.g., biopotentials), a stimulator 204 forgenerating pacing signals, and a signal processor 206 coupled to thesensor 202 and the stimulator 204. The sensor 202 can be a monopolarsensor or a bipolar sensor, and is carried on a structure (not shown),such as a catheter, a probe, or an expandable device (e.g., a basket ora balloon). In other embodiments, the system 200 can include more thanone sensor. In the illustrated embodiments, the stimulator 204 isconfigured to generate pace signals at a rate that is faster than acycle of a cardiac signal. For example, if a cardiac signal cycle is 250milliseconds (ms), the stimulator 204 can be configured to generate apace signal every 240 ms, thereby allowing a cardiac signal to be“captured”. In some embodiments, the stimulator 204 can be integratedwith the sensor 202, in which cases, the sensor 202 can be used to emitpace signals and sense biopotentials. The signal processor 206 isconfigured to receive a sensed cardiac signal from the sensor 202 and apace signal from the stimulator 204, and generate a feedback based atleast in part on the received cardiac signal and the pace signal. Thesignal processor 206 will be described in further detail below.

In the illustrated embodiments, the mapping system 200 further includesan amplifier 208 for amplifying sensed cardiac signals before they aretransmitted to the signal processor 206. In some embodiments, theamplifier 208 can be implemented as a component of a recorder, whichrecords or temporarily save biopotential signals for later use. Inalternative embodiments, the amplifier 208 can be implemented as acomponent of the catheter. In further embodiments, the amplifier 208 isoptional, and the system 200 does not include the amplifier 208.

The signal processor 206 includes a pace-signal detector 230 fordetecting a pace signal generated by the stimulator 204, ananalog-to-digital (A/D) converter 232 for converting signals intodigital format, a filtering module 234, and a caliper module 236. Inother embodiments, the pace-signal detector 230 can be implemented as acomponent of the stimulator 202, in which case, the signal processor 206does not include the pace-signal detector 230. Also, in otherembodiments, signals received from the sensor 202 are already in digitalformat, in which cases, the A/D converter 232 is configured to convertpace signals into digital format, and sensed cardiac signals are passeddirectly from the pace-signal detector 230 to the filtering module 234.Alternatively, signals received from the stimulator 204 are already indigital format, in which case, the A/D converter 232 is configured toconvert sensed cardiac signals into digital format, and detected pacesignals are passed directly from the amplifier 208 to the filteringmodule 234. In further embodiments, signals received from both thesensor 202 and from the stimulator 204 are already in digital format, inwhich case, the signal processor 206 does not include the A/D converter232, and signals received from the sensor 202 and the stimulator 204 arepassed directly to the filtering module 234.

The filtering module 234 is configured to apply a dynamic filter toeliminate any baseline shift of a pace channel that could obscurepost-pacing signal recovery, while preserving low frequency signalcontent in a recorded biopotential. In the illustrated embodiments, thefiltering module 234 is configured to apply a high pass filter having afirst 3DB point value. When the pace-signal detector 230 detects a pacesignal, the filtering module 234 toggles the first 3DB point value to asecond 3DB point value, and maintain the high pass filter at the second3DB point value for a prescribed duration dT. After the prescribedduration dT has lapsed, the dynamic filter is then toggled back from thesecond 3DB point value to the first 3DB point value. The prescribedduration dT can be, for example, any value that is between approximately10 milliseconds (ms) and 100 ms, and more preferably, betweenapproximately 10 ms and approximately 50 ms. However, the prescribedduration dT can be a different value in alternative embodiments,depending on the particular application.

As used in this specification, the term “3DB point value” refers to acharacterization of a filter's frequency response. For example, a unitygain high pass filter having a 3DB point value of 30 Hertz (i.e., a 30Hertz high pass filter) will have a gain of 0.707 at 30 Hz. As such, asignal having a frequency that is higher than 30 Hertz will have acorresponding gain that is higher than 0.707, while a signal having afrequency that is lower than 30 Hertz will have a corresponding gainthat is lower than 0.707. In the illustrated embodiments, the first 3DBpoint value can be a value that is between approximately 0.5 hertz (Hz)and 50 Hz, and more preferably, between approximately 20 Hz and 40 Hz(e.g., 30 Hz), and the second 3DB point value can be a value that isbetween approximately 80 Hz and 120 Hz, and more preferably, between 90Hz and 110 Hz (e.g., 100 Hz). In other embodiments, the first 3DB pointvalue can be zero. In further embodiments, the filtering module 234 canbe configured to toggle the filter between a first 3DB point value and asecond 3DB point value that are different from the values describedpreviously.

Toggling the dynamic high pass filter from the first 3DB point value tothe second 3DB point value provides a better step response, and togglingthe dynamic high pass filter back to the first 3DB point value allows afull bandwidth of biosignal be captured after obtaining the better stepresponse.

In the illustrated embodiments, the filtering module 234 is configuredto toggle the dynamic high pass filter from a first 3DB point value to asecond 3DB point value at every detected pace signal. Alternatively, auser interface can be provided that allows a user to control thefiltering module 234 such that the filter is toggled from the first 3DBpoint value to the second 3DB point value for the prescribed durationfor a detected pace signal selected by the user. In some embodiments,the signal processor 206 also includes a user interface (e.g., a buttonor a control) which allows a user to select the first value, the secondvalue, and/or the duration dT. Alternatively, the first 3DB point value,the second 3DB point value, and/or the duration dT can be default valuesset by a manufacturer of the signal processor 206. The filtering module234 can be implemented using software, hardware, or a combination ofsoftware and hardware, using techniques known in the art.

In other embodiments, the filtering module 234 can be configured toapply a median filter to the response signals. With a median filter, theboxcar width is less than half the width of the narrowest expectedelectrogram. In a preferred embodiment, the width is between 10 ms and20 ms. Applying a median filter distorts the shape of the waveform of anelectrogram, but leaves the width of the electrogram unmodified.

In further embodiments, the filtering module 234 can be configured toapply a low-pass filter to the response signals. Low-pass filteringprovides several benefits. This filtering process tends to decrease theeffects of noise and removes near-zero values. The median filter isrelatively tolerant to such low values. Electrogram durations will bebiased to lower numbers without the low-pass filters. Also, if themedian filter is chosen to be quite narrow, e.g. 5 ms, electrogramduration can be measured to be much shorter than it would be if measuredmanually by an expert electrophysiologist. Conventional low-passfiltering tends to widen the processed signal. Therefore, if a box-caraveraging method is used, the measured duration of the processed signalneeds to be decreased by the width of the boxcar used for filtering.Various other low-pass filtering procedures may be used. For a givenfilter, however, the duration measured generally needs to be adjusteddownward by the width of the filter's impulse response.

In general, any filtering performed by the filtering module 234 can beaccomplished by an appropriately programmed computer/processor ordedicated hardware designed to perform one or more signalprocessing/filtering functions.

In the illustrated embodiments, when a pace signal is detected by thepace-signal detector 230, the caliper module 236 is also activated tomeasure a duration between the detected pace signal and a next detectedbiopotential, thereby obtaining a post-pacing interval (PPI). FIGS. 3and 4 illustrate logics 300 of the filtering module 234 and the calipermodule 236 in accordance with embodiments of the invention. As shown inFIGS. 3 and 4, the filtering module 234 is configured to toggle adynamic filter between a first 3DB point (e.g., 30 Hz) to a second 3DBpoint (e.g., a 100 Hz) for a prescribed duration dT when a pace signalis detected (See filter timing graphs 302). If the filtering module 234is configured to toggle the dynamic filter every time when a pace signalis detected, the caliper module 236 can be configured to obtain a PPIvalue for every detected pace signal (See caliper timing graph 304 inFIG. 3). Alternatively, a physician can use the interface describedpreviously to select a detected pace signal as a reference 402, based onwhich, the caliper module 236 will obtain a PPI value. In such case, thecaliper module 236 is activated to obtain the PPI associated with theselected pace signal (See caliper timing graph 400 in FIG. 4B). Usingthe caliper module 236 to automatically obtain PPI value(s) isadvantageous because it obviates the need for a physician to manuallymanipulate software and/or data to obtain the PPI value(s), which can betime consuming and subjected to human errors.

In order for the caliper module 236 to automatically determinepost-pacing intervals, electrogram complexes need to be identified in arecording channel before measuring or estimating response signalinterval. Automatic detection of biological signal complexes with shortdurations and fast repetition rates has been studied and reported inboth scientific publications and in patent disclosures. Also, signalprocessing of electrograms including ECGs (electrocardiograms), EEGs,and other biological signals generally is well-known. Two publicationsdescribing automatic detection of the ECG waveform are: (1) “Holtertriage ambulatory ECG analysis: Accuracy and time efficiency,” Cooper etal., J Electrocardiol., 1(1), pp. 33-38, 1996; and (2) “On the detectionof QRS variations in the ECG,” Shaw et al., IEEE Trans Biomed Eng.,42(7), pp. 736-741, 1995.

In general, all electrogram complexes have multiple peaks and zerocrossings. A duration of a signal or an electrogram is defined herein tomean the time from the first “significant” deviation from the recordingbaseline to time at which no further “significant” deviation isobserved. This definition of electrogram duration results in anon-stationary value for duration as noise is added to the system. Thatis, the duration becomes shorter as the signal is corrupted by morenoise. For normal electrogram recordings, noise is small compared to theelectrogram signal, resulting in duration determinations very close tothose that would be obtained in a noise-free environment. Forfractionated electrograms which may result from a slow conduction zone,however, noise can be significant. Therefore, signals with as low anoise level as possible is sought, and signal processing is applied toreduce the effects of noise in accordance with embodiments of theinvention. In some embodiments, all signals with values above athreshold level are considered significant and become a part of anelectrogram complex. One method of finding the beginning and end of thecomplex is to search backward and forward from the peak of the processedsignal to find the first occurrences of signals below the threshold tofind the beginning and end of the complex, respectively.

The threshold can be defined in various ways. In one embodiment, thethreshold is defined in terms of percentage of the peak electrogramamplitude. In another embodiment, the threshold is defined as a fixedsignal amplitude, such as 0.1 millivolt (mV). In a preferred embodiment,the threshold is defined as a value based on characteristics of thesignal being recorded, i.e., an adaptive threshold. An adaptivethreshold value may be the median value of all processed signal valuesthat are not within the electrogram complex. If the electrogram durationis less than about 25% of the pacing cycle length, the median value forall processed signal values is commonly nearly the same as the medianvalue of all non-complex processed signals. In this usual case, themedian value for all processed signal values can be used for thethreshold. This is the case since in normal tissue, most signals arenear the iso-electric line, i.e., the signals are very small. In theabove-described method, it is valuable to process the signal values foreach heart beat separately, using signal segments from 1 to 1½ cyclelengths long. Signal segments including more than one complete cyclereduces the probability that the signal segment will begin or end in themiddle of an electrogram complex. When relatively short signal segmentsare used for analysis (e.g. 1 to 1½ cycle lengths long), sorting theprocessed signal values in amplitude order, while maintaining pointersto the time location for each signal value, provides a simple means toimplement the above-described method for determining electrogramduration. First, choose the median of the entire processed signalsegment as the initial threshold. Then, use the time location of thelargest signal to begin a forward and backward search in the processedsignal for the beginning and end of the complex. If the complex durationis less than ¼ the cycle length, then stop. If the width of the complexis greater than ¼ the cycle length, redefine the threshold as the medianof non-complex values and repeat the search. For longer complexdurations, this iteration need not be done more than two to three times,since the solution rapidly converges. For each iteration step, the newthreshold can be read directly from the original sorted file, since bydefinition, all values in the complex were above the original value forthe threshold. In addition, if the beginning and ending locations weresaved, the search for the newly-defined beginning and end of the complexcan begin at the saved locations. Each iteration results in an increaseor no change in measured electrogram duration. The iteration terminateswhen no change in duration occurs. Other methods for defining thethreshold value to determine the electrogram complex duration can beemployed.

Pacing artifacts can significantly complicate the task of automaticallydetermining PPI, especially for electrode pairs close to the pacingsites. This is because the pacing artifacts are temporally close to thebeginning of the electrogram complex. There are several ways to overcomethe interference of the pacing artifacts and to simplify the task ofdetermining the beginning of each electrogram complex. In someembodiments, signals recorded while pacing signals are applied and for 1to 2 milliseconds after the termination of pacing signal application areignored. Since the pacing artifact is propagated electrically, thepacing artifact is synchronous in all recording channels. Therefore, oneapproach is simply to ignore all signals that are recorded during thepacing. In other embodiments, the effects of pacing artifacts can bereduced or eliminated entirely using either nonlinear or adaptivefiltering techniques. These techniques are described in U.S. Pat. No.5,601,088 which is incorporated in its entirety by reference. In otherembodiments, response signals from electrodes located near theelectrodes used in pacing are ignored. Since response signals frommultiple pacing locations are measured, it is possible to ignore someelectrode locations near each pacing site. In other embodiments,response signals from electrodes that are used to apply the pacingsignals are ignored. If the electrode is connected to the system forrecording during pacing, the input amplifiers are saturated during andfor some time after the pacing pulse has terminated. The time to recoverfrom saturation varies by recorder system manufacturer and for differentmodels of recorder systems produced by the same manufacturer. Even forsystems with fast recovery from saturation, electrograms recorded frompacing electrodes tend to be greatly distorted for 10 ms to 100 ms afterpacing due to after-potentials at the electrode-electrolyte interfacefollowing pacing. In further embodiments, the recorder system can bedisconnected from all electrodes during the delivery of the pacingsignals. For many recorder systems, this would eliminate the pacingartifacts in all recording channels, except for residual artifactsignals due to after-potentials which is seen on all channels using thepacing electrode(s).

As discussed previously, applying a dynamic filter can eliminate anybaseline shift of a pace channel that could obscure post-pacing signalrecovery, while preserving low frequency signal content in a recordedbiopotential. FIG. 5 shows an example of an electrogram 500 having datathat have been processed by the filtering module 234. The electrogram500 includes biopotential data 502, which is within a view window 504presented to a user. As such, the biopotential data 502 is not “lost” asa result of the filtering. FIG. 5 also shows a PPI value 510 that isbeing automatically determined by the caliper module 236.

In the some embodiments, the signal processor 206 can further include anoutput interface for presenting information to a user. For example, thesignal processor 206 can include a display screen for displaying PPIvalue(s), or an audio speaker for reporting PPI value(s). Alternatively,instead of an output interface, the signal processor 206 can be coupledto a memory to which PPI value(s) can be stored for later retrieval. Infurther embodiments, the signal processor 206 can be coupled to anablation device/system, which controls an ablation process based onsignals received from the signal processor 206. For example, when a PPIvalue indicates that a target ablation site has been located, theablation device/system then delivers ablation energy to ablate targettissue at the ablation site.

It should be noted that any of the components (e.g., the pace-signaldetector 230, the A/D converter 232, the filtering module 234, and thecaliper module 236) of the signal processor 206 can be implemented usingsoftware, hardware, or a combination of software and hardware. Inaddition, although the pace-signal detector 230, the A/D converter 232,the filtering module 234, and the caliper module 236 are illustrated asseparate components, in other embodiments, one or more of thesecomponents can be integrated with another one of these components. Forexample, in other embodiments, the filtering module 234 and the calipermodule 236 can be implemented as a single unit.

Although the signal processor 206 has been described as having filteringand PPI measuring capabilities, in other embodiments, the signalprocessor 206 can also perform other functions to improve the accuracyof a PPI measurement. In some embodiments, where the heart is stimulatedmultiple times under the same condition, ensemble averaging is used toimprove the effective signal-to-noise ratio. For example, if the heartis paced four times, fiducial points (i.e., identifiable features in acomplex that are used as time references) for four complexes from eachrecording can be aligned and used to ensemble average four beats fromeach channel, thereby increasing the signal-to-noise level by a factorof two in each channel.

The above described system 200 and method can significantly improve anentrainment pacing procedure. Entrainment pacing assesses functionalparticipation of a tissue site in the reentrant pathway of a conductionzone. Entrainment involves continuous resetting of the reentrant pathwayby stimulating and capturing tissue in the pathway. Tachycardia, or fastbeating of the heart, can be entrained in this manner if the tachycardiais caused by a reentrant pathway. FIG. 6A illustrates this concept.Panel 1 shows a hypothetical slow conduction zone 690 and a reentrantpathway 692 around the slow conduction zone 690. Panels 2 and 3 show theeffects of a single stimulus at site R. Site R is remote from thereentrant pathway 692. The stimulus captures and excitation wavespropagate out in all directions 694 from the stimulus site R 696. Thewavefronts 695 traveling from the stimulus site R 696 to site B travelsin a direction opposite to the wavefronts in the reentrant pathway 692.These wavefronts 695 from site R 696 are called antidromic wavefronts.Site B is depolarized by the antidromic wavefronts 695. The wavefronts693 from site R traveling to site C travels in the same direction as thewavefronts in the reentrant pathway 692. The wavefronts 693 traveling tosite C are called orthodromic wavefronts. Site C is depolarized by thepremature orthodromic wavefronts. An electrogram recorded from this siteretains a similar morphology to the electrograms recorded duringtachycardia. Panel 3 shows that a new reentrant pathway 692′ includessite R 696.

The post-pacing interval determined using embodiments of the inventioncan be analyzed to determine whether a tissue site is near the slowconduction zone or in the reentrant pathway. As discussed previously,the post-pacing interval is the interval from the time when a tissuesite is stimulated (e.g., as represented by a detection of a pacesignal) to the time when the next nonstimulated depolarization followingthe stimulus is measured (e.g., as represented by a detection of abiopotential). At the pacing site FIG. 6B shows a two-loop reentrantpathway. Referring to FIG. 6B, if a site 698 in the reentrant pathway692 is paced, the depolarization following the stimulus is thestimulated orthodromic wavefront 697 after it has propagated through thepathway 692, and returned back to the pacing site 698. This is therevolution time through the pathway 692 and equals the tachycardia cyclelength. Referring to FIG. 6B, if a site 696 remote from the reentrantpathway 692 (site R) is paced, the post-pacing interval is theconduction time from the stimulus site 696 to the reentrant pathway 692,through the pathway and back to the pacing site 696. Thus, thepost-pacing interval exceeds the tachycardia cycle length when a siteoutside the reentrant pathway is entrained. A minimum difference betweenthe post-pacing interval and tachycardia cycle length of 30 millisecondsor less is associated with an increased likelihood that the ablation atthe site will interrupt the tachycardia. Entrainment pacing is describedin “Entrainment Techniques for Mapping Atrial and VTs,” Stevenson etal., J Cardiovasc Electrophysiol, Vol. 6, pp. 201-216, March 1995.

Once it is determined that a monitoring electrode is located in areentrant pathway, the tissue near the monitoring electrode is destroyedby creating a lesion having a prescribed characteristics, e.g., surfacearea, width, and/or depth.

Computer System Architecture

FIG. 7 is a block diagram that illustrates an embodiment of a computersystem 700 upon which embodiments of the invention may be implemented.Computer system 700 includes a bus 702 or other communication mechanismfor communicating information, and a processor 704 coupled with the bus702 for processing information. The processor 704 may be configured toperform any of the functions described herein. The computer system 700also includes a main memory 706, such as a random access memory (RAM) orother dynamic storage device, coupled to the bus 702 for storinginformation and instructions to be executed by the processor 704. Themain memory 706 also may be used for storing temporary variables orother intermediate information during execution of instructions to beexecuted by the processor 704. The computer system 700 further includesa read only memory (ROM) 708 or other static storage device coupled tothe bus 702 for storing static information and instructions for theprocessor 704. A data storage device 710, such as a magnetic disk oroptical disk, is provided and coupled to the bus 702 for storinginformation and instructions.

The computer system 700 may be coupled via the bus 702 to a display 712,such as a cathode ray tube (CRT), for displaying information, such asbiopotential data or electrogram, to a user. An input device 714,including alphanumeric and other keys, is coupled to the bus 702 forcommunicating information and command selections to processor 704.Another type of user input device is cursor control 716, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 704 and for controllingcursor movement on display 712. This input device typically has twodegrees of freedom in two axes, a first axis (e.g., x) and a second axis(e.g., y), that allows the device to specify positions in a plane.

Embodiments of the invention is related to the use of computer system700 for collecting and processing data. According to one embodiment ofthe invention, such use is provided by computer system 700 in responseto processor 704 executing one or more sequences of one or moreinstructions contained in the main memory 706. Such instructions may beread into the main memory 706 from another computer-readable medium,such as storage device 710. Execution of the sequences of instructionscontained in the main memory 706 causes the processor 704 to perform theprocess steps described herein. One or more processors in amulti-processing arrangement may also be employed to execute thesequences of instructions contained in the main memory 706. Inalternative embodiments, hard-wired circuitry may be used in place of orin combination with software instructions to implement the invention.Thus, embodiments of the invention are not limited to any specificcombination of hardware circuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to the processor 704 forexecution. Such a medium may take many forms, including but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media includes, for example, optical or magnetic disks,such as the storage device 710. Volatile media includes dynamic memory,such as the main memory 706. Transmission media includes coaxial cables,copper wire and fiber optics, including the wires that comprise the bus702. Transmission media can also take the form of acoustic or lightwaves, such as those generated during radio wave and infrared datacommunications.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to the processor 704 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to the computer system 700can receive the data on the telephone line and use an infraredtransmitter to convert the data to an infrared signal. An infrareddetector coupled to the bus 702 can receive the data carried in theinfrared signal and place the data on the bus 702. The bus 702 carriesthe data to the main memory 706, from which the processor 704 retrievesand executes the instructions. The instructions received by the mainmemory 706 may optionally be stored on the storage device 710 eitherbefore or after execution by the processor 704.

The computer system 700 also includes a communication interface 718coupled to the bus 702. The communication interface 718 provides atwo-way data communication coupling to a network link 720 that isconnected to a local network 722. For example, the communicationinterface 718 may be an integrated services digital network (ISDN) cardor a modem to provide a data communication connection to a correspondingtype of telephone line. As another example, the communication interface718 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, the communication interface 718sends and receives electrical, electromagnetic or optical signals thatcarry data streams representing various types of information.

The network link 720 typically provides data communication through oneor more networks to other devices. For example, the network link 720 mayprovide a connection through local network 722 to a host computer 724 orto another equipment 726. The data streams transported over the networklink 720 can compose electrical, electromagnetic or optical signals. Thesignals through the various networks and the signals on the network link720 and through the communication interface 718, which carry data to andfrom the computer system 700, are exemplary forms of carrier wavestransporting the information. The computer system 700 can send messagesand receive data, including program code, through the network(s), thenetwork link 720, and the communication interface 718.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. For example, in alternative embodiments, insteadof using the signal processor 206 to obtain post pacing interval data,the signal processor 206 can be used to automatically obtain other typesof data. In addition, an illustrated embodiment needs not have all theaspects or advantages of the invention shown. An aspect or an advantagedescribed in conjunction with a particular embodiment of the presentinvention is not necessarily limited to that embodiment and can bepracticed in any other embodiments of the present invention even if notso illustrated. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

1. A system for processing a biopotential signal, comprising: a detectorfor detecting a pacing signal; and a filtering module for applying adynamic filter based on the detected pacing signal. 2-39. (canceled)